This invention relates to a system for diagnosing faulty check valve operation in an internal combustion engine having a back flow preventing check valve positioned in each air intake passage leading to an engine cylinder.
It is generally known that at high operating speeds, the performance of a four-stroke internal combustion engine can be improved by advancing the opening and retarding the closing of cylinder intake valves during the engine operating cycle. Opening a cylinder intake valve early, while its respective exhaust valve is still open (known as cross-over), facilitates the discharge of gaseous combustion products from the cylinder at high engine speeds, while delaying the closing of the intake valve, until after beginning of cylinder compression, improves cylinder filling.
Both of the above valve timing modifications improve high speed engine performance, however, the torque produced at low speeds is significantly reduced. This occurs because the inertia of the intake air inducted into the engine decreases at low engine speeds. As a result, a portion of the air-fuel charge in each cylinder is driven back into the air induction system at low engine speeds, due to the delayed intake valve closing. In addition, when the engine is operated under light loading conditions, exhaust products are able to flow from the exhaust system back into the engine cylinders and air induction system during the cross-over period. This can result in cylinder misfires and rough engine idling.
It is also generally known that the above low speed drawbacks can be obviated by placing check valves in the engine air induction system. These check valves are typically placed downstream of the air intake throttle valve, in each air passage leading to an engine cylinder. Each check valve is positioned to allow air flow in a direction toward its associated cylinder, but prevent back flow in the opposite direction, away from the cylinder. Consequently, engine volumetric efficiency and torque output are greatly improved at low speeds and combustion stability is improved under light engine loading conditions.
In this type of engine, if one of the intake passage check valves becomes damaged or malfunctions, the engine will not perform properly at low speeds. The back flow of exhaust gas into the associated cylinder can cause misfires and rough engine idling. Also, the decreased volumetric efficiency of the cylinder reduces the output torque. In addition, the cylinder associated with the faulty check valve will receive less air, while the other cylinders receive excess air. This produces incorrect cylinder air-fuel mixtures and increases engine exhaust emissions.
Consequently, there exists a need for a system, which is capable of diagnosing and indicating faulty check valve operation in engines equipped with such valves, to ensure proper engine performance and low exhaust emissions.